Evaluation of species-specific score cut-off values for various Staphylococcus species using a MALDI Biotyper-based identification

Abstract

Although previous studies investigating the MALDI Biotyper database (matrix-assisted laser desorption/ionization time-of-flight mass spectrometry-based identification) have proven its high accuracy for bacterial identification, the studies differed in sample preparation, number of replicates, quantity of shots and target types used. In particular, the score cut-off values of special importance for reliable species identification varied. The aim of the present study was to identify species-specific differences in the mean score values for staphylococci. Cut-off values recommended by the manufacturer were adapted using the 20th percentile to rule out unknown score-modifying factors, even though the specificity was high and the lowest cut-off values would also yield an accurate result. Whilst correct species diagnosis was obtained in 97.32 % of samples (1382/1420), only 220 of all duplicates (15.49 %) revealed a score of ¢2.3, whilst 968 (68.17 %) had a score between 2.0 and 2.299, and 194 (13.66 %) had a score of ,2.0. Ten of 21 species had a calculated 20th percentile of ,2.0 and one species of ,1.7. In conclusion, the use of species-specific cut-off values improves the relative sensitivity of species identification in staphylococci.

MALDI-TOF mass spectrometry following short incubation on a solid medium is a valuable tool for rapid pathogen identification from positive blood cultures

“…Our previous experience in MALDI-TOF MS analyses suggested that the manufacturer-recommended confidence score thresholds for species might be overly conservative (Richter et al, 2012;Szabados et al, 2012). This was confirmed by reports on MALDI-TOF MS performed directly from positive blood cultures, as rates of concordance to species were similar using lower cut-off values compared to the manufacturer-recommended ones (Buchan et al, 2012;Christner et al, 2010;Klein et al, 2012;Lagace-Wiens et al, 2012;Prod'hom et al, 2010;Schubert et al, 2011).…”

“…Our prior studies indicated that the manufacturerrecommended MALDI-TOF MS confidence score thresholds for identification to the species level may be overly conservative (Richter et al, 2012;Szabados et al, 2012). Consequently, we applied different cut-off values for species identification (≥1.3 to ≥2.0) to the MALDI-TOF MS analyses performed for the 325 study isolates derived from monomicrobial blood cultures (Fig.…”

Application of Matrix-assisted Laser Desorption Ionization Time-of-flight Mass Spectrometry for Identification of Coagulase-negative Staphylococci Isolated from Milk of Cows with Subclinical Mastitis

“…The manufacturer suggested a score ≥2.300 was needed for secure species identification, and 2.000-2.299 for secure genus but probable species identification. However, in practice, lower scores have been suggested as acceptable for species level identification (Richter et al 2012. For example, one study with ethanol/formic acid extraction suggested using scores of ≥2.0 for secure species identification of S. aureus, S.…”

“…For example, one study with ethanol/formic acid extraction suggested using scores of ≥2.0 for secure species identification of S. aureus, S. capitis, S. epidermidis, S. hominis, S. lugdunensis, S. saprophyticus, and S. simulans, and a score of 1.7 as sufficient for identification of S. caprae, S. sciuri, and S. cohnii (Richter et al 2012). This suggests that the species-specific score cutoff values may require additional optimization or more extensive representation in the database (Zhu et al 2015).…”

Evaluation of the Biotyper MALDI-TOF MS system for identification of Staphylococcus species

“…The relative ease of use, speed and cost effectiveness has generated substantial interest in the use of MALDI-TOF MS for identification of various microorganisms, including bacteria and fungi (Clark et al, 2013;Dubois et al, 2012;Szabados et al, 2012). While several reports have described the use of MALDI-TOF MS for the identification of Staphylococcus species, these studies have differed in sample preparation methods, diversity of species represented, number of replicates tested, reference identification methods, and interpretive criteria used (Clark et al, 2013;Dubois et al, 2010;Matsuda et al, 2012;Richter et al, 2012;Szabados et al, 2012).…”